In the offline disk media servo-writing scheme, the servo writing process is carried out before the disks are placed inside the hard drive. The disks are servo-written on dedicate equipment (media servowriter) in a cleanroom. One advantage of this scheme is that multiple disks can be servo written at any one time using the same set of hardware. In addition, as hard drives nowadays usually contain only one to two disks, in-drive servo-writing can take up a lot of cleanroom space and time. By servo-writing multiple disks outside the hard drive, the usage of cleanroom space and time can be substantially reduced.
The capacity of disk data storage devices has been increasing 30% every year for the last 20 years. One way to achieve this exponential growth of storage capacity is to keep increasing the data track density. In a current disk drive, the data track distance is around 0.000008″ from track to track. There is also a need to spin disk stack faster to increase the data input/output throughput. Under the conditions of shrinking distance between tracks and increasing speed of spins of disk stack, the vibration reduction of disk stack during servo writing is essential to meet error rate performance requirements.
In a typical media servowriter, disks are stacked and packed in a hub that is attached to the rotating shaft of an air-bearing spindle motor. During servo-track writing, the rotary motion of the spindle shaft spins the hub and hence the disk pack it carries. Each read-write head is attached to a head suspension device that is connected to an actuator arm. The actuator arms carrying the read-write heads are inserted in-between the disks while reading or writing on the disk surfaces. The suspension, taking the form of a flat sheet of steel, has a bend that creates a spring mechanism to press the read-write head onto the disk surface. The read-write heads are, however, prevented from touching the disk surfaces by a layer of air current flowing beneath the heads when the disks are spinning.
It has been recognized that the air current flowing in-between spinning disks not only lifts up the read-write heads but also generates large quantity of air turbulence in the vicinity of the read-write heads at the same time. These strong air currents can agitate the actuator arms that carry the read-write heads, and shake the heads off their intended positions. The strong air currents can also push against the disk surfaces, inducing additional undesirable vibrations to the spinning disks.
There are some attempts made to address the problem of air currents generated in-between spinning disks in a media servowriter. U.S. Pat. No. 6,097,568 provides a data storage device with air dams to interrupt circumferential airflow near the surface of one or more spinning disks. The air dams are an array of fingers, where each finger is projected into the gap between two spinning disks so as to interrupt the airflow and reduce the likelihood of local turbulence and disk vibration.
U.S. Pat. No. 6,600,625 provides a disk drive with a fluid deflector for reducing fluid turbulence near a transducer device. The fluid deflector includes a deflector finger in close proximity to the slider of disk drive read/write head in order to reduce the fluid turbulence near transducer only. It does not address the problem of disk vibration.
U.S. Pat. No. 6,785,082 provides a disc drive servo track writer with a sealing camber filled with low density gas. When the disks are spin within the sealed chamber, it is believed that the low density gas causes lower vibration force for the spinning disks in comparison with operations under normal atmosphere condition. However, it requires complicate and expensive sealing scheme and tedious and time-consuming procedure to reclaim the low density gas. In addition, the benefit of disk vibration reduction resulting from using of low density gas is limited since the nature of gas turbulence is still there.
U.S. Pat. No. 6,788,493 discloses a fluid diffuser for reducing fluid velocity near disk surfaces in a rotating disk storage device. The fluid diffuser includes one or more stationary diffuse wings, where one or more of the diffuser wings can extend between two of the storage disks. The diffuser wings are strategically located on the upstream of read/write head slider and hopefully to reduce air speed such that to have less “chance” to affect flying head slider and incur vibration.
U.S. Pat. No. 6,801,387 discloses methods to reduce the whirling air vortices which are normally formed at the disc tip. For example, the outer edge of the disc surface may be gradually thinned down to a sharp tip; a flow obstruction may be incorporated in the shroud adjacent the edge of the disc tip.
In yet another prior art, the air baffle is a solid metal block with separate circular slot trenches for individual disks. The air baffle is fully closed on all side ends except the one end for introducing the disks stack into the baffle. The air volume between any two disks on the disk stack is minimized to reduce the amount of air currents. However, due to the closed side ends, substantial amount of air currents can be present at the side end that is left open. Fabrication of such an air baffle is also a difficult task, as it requires precise removal of material in thin and yet deep trenches. Cutting blades easily get caught in the removal process and break off. Due to the tight dimensional tolerance required for the slot trenches, the half-done block of metal has to be scraped and the machining process restarted using a new metal block. This increases the cost of fabricating such an air baffle tremendously